Hi,
I have worked with crowned plovers, blacksmith plovers , southern lapwings, ringed plovers and northern lapwings. They are lovely birds to work with !
We kept them in pairs as the only ground birds as they get very territorial and bonded pairs will often kill other plovers and other smaller ground birds!! All the species except the crowned plovers are water birds so were given access to running water for bathing and foraging. A lot of wading birds can get problems with their feet and are susceptible to bumble foot and other infections, for these reasons they were kept on soft substrates such as leaf litter, sand, fine gravel and soft bark which was raked and forked daily. Their favourite roosting areas where also cleaned daily as they often defecate here also increasing the risk of them getting infections.
The more tropical species such as the blacksmiths and the crowned plovers were kept in sheltered aviaries with access to heated sheds in the winter as in can get quite cold here in England and they can be susceptible to frost bite.
Diets consisted of a insectivorous mixture as a base Bogena was the brand we used the most, a meat based dog food chopped up into small pieces ( forth glade was used ), chopped cold water prawns and a small amount of fruit ( mostly for the softbills they shared their aviaries with but they did eat it from time to time). This diet was also supplemented with live food three times a day ( which increased to five times when they had chicks), consisting of mealworms marioworms wax worms and crickets. Small amounts of tuna and lamb mince were also added when we had some left over from the ibis diets. Plovers can also be fed based on a pelleted diet formulated by mazuri, however we never had enough plovers to make it affordable and our plovers did very well on the diet!
We bred the blacksmith and crowned plovers multiple times each year however we had limited success with the others as we had single sexes of the ringed plovers and northern lapwings and they southern lapwings never laid fertile eggs.
In 2014 we successfully hand reared five blacksmith plover chicks( as they adults shared an aviary with azure winged magpies) and parent reared four chicks, aswell as parent rearing four crowned plover chicks. When rearing the chicks we found the use us of calcium supplements and lots of exercise was necessary as with any long legged species they can be prone to leg deformations such as leg bowing and bending at the joints.
I loved the plovers so much I bought a female blacksmith plover who now lives with my wildfowl. She cost £150 and I've seen pairs for £300-350. Masked plovers are a bit cheaper at £250 a pair!
Hope this has been helpful !! If you have any other questions please ask,
Will

All species are fine when kept with most other birds outside the breeding season, this does change when breeding. It is dependent on the individual pair tbh not the species, i found that particularly prolific pairs were the most aggressive to other birds.
We successfully kept pairs of blacksmith plovers, crowned plovers and northern lapwings( N. lapwings were same sex pairs though) with ground doves, redshank and Madagascan teal, however these plovers never bred. Single birds are normally 100% fine with other ground dwelling aviary companions.
It also depends on how big the aviary is and the lay out off the aviary. If there is a large area of water a waterfowl plover mix may be alright, or if the aviary is split into two areas of land by a separating body of water, giving the plovers one area to be protective over and the ducks another area. Clever agricultural techniques can often over come the plovers aggressive tendencies.
Hope this is helpful,
Will

Sounds like a nice sized pen, should be fine to add a pair of masked plovers to it as long a it isn't overstocked with wildfowl. Try and add some features that provide visual blocks between the birds, that should help reduce aggression between birds. As long as you watch how the plovers act during the breeding season im sure it will be fine!!!
Good luck,
will